The intent of this research is to determine how cGMP, in combination with LH, may be involved in the mechanism of oocyte maturation. The thrust of these studies centers on 1) How cGMP acts in conjunction with LH to stimulate oocyte maturation and 2) What substances regulate cGMP levels in the ovary and are these levels functionally related to the maturational event? The first series of experiments will study the temporal sequence of how oocyte maturation is affected by elevated levels of cGMP. This will be determined both in follicle-enclosed oocytes stimulated by LH and in spontaneously maturing oocytes. Cyclic AMP and cGMP levels will be measured in the various cell types following different treatments to determine how each cyclic neucleotide may be influencing the other and the maturation process. Our previous work indicates that cGMP may be stimulating cAMP-phosphodiesterase (cAMP-PDE). Several studies will measure the effects of cGMP on changes in oocyte and follicle cell cAMP over time. This will be done by first elevating cAMP levels in the cumulus cells alone (using LH) or the cumulus cells and the oocyte (using forskolin). After a short incubation period, the cells are changed to medium without forskolin or LH and the rate of cAMP decline will be observed in the presence or absence of high cGMP concentrations. If cGMP is stimulating cAMP-PDE it may increase the rate of decline in cAMP levels in the oocyte and follicle cells. The effects of cyclohexamide on cGMP-augmented oocyte maturation will be tested to determine whether protein synthesis is playing a role in this process. Finally, cAMP-PDE activity will be measured in follicle cells and oocytes to further determine if the observed effects of cGMP on oocyte maturation may be mediated through this enzyme. It is possible that cGMP in conjunction with LH is causing a decrease in the levels of oocyte and cumulus cell cAMP. The decline in oocyte cAMP is postulated to be a possible mechanism for the initiation of oocyte maturation. Therefore, if cGMP is acting physiologically to reduce cAMP levels in the oocyte at the time of the LH surge, it may be an important modulator in the process of oocyte maturation. Additional studies will examine what factors may be regulating cGMP levels in the cell. These experiments will measure the effects of such substances as follicular fluid, fibroblast growth factor and prostaglandins on guanylate cyclase.